Put the reply text inside question notification emails

The notification only said that the school had answered and linked into
the LMS, so a student had to log in to read two lines. Delivered mail
plus an unread thread was the common outcome — one such thread was a
pre-sale question that never converted.

The mail now carries the answer itself (capped at 2000 chars, with a
pointer to the thread when longer or when files are attached). Quoted
blocks are HTML-escaped, which they were not before.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/app/api/questions/[id]/messages/route.ts

@@ -78,6 +78,8 @@ export async function POST(
       question.user.name,
       question.title,
       id,
+      text.trim(),
+      Boolean(safeFiles?.length),
     );
   } else {
     const staff = await prisma.user.findMany({